Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241317 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 917 AM EDT Mon Jul 24 2017 .SYNOPSIS... A cold front will approach the area today before passing through tonight. High pressure will build into the area Tuesday before moving offshore Wednesday. Another cold front will approach the area Thursday before passing through Friday into Friday night. High pressure may return for the weekend. && .NEAR TERM /TODAY/... Low pressure over PA with an attendant cold front over WV. The front will move across the region late this afternoon and evening. A mix of sun and clouds is expected into the afternoon. Temperatures expected to rise back into the upper 80s and low 90s, and with dew points from the mid 60s to low 70s. We`ll see heat indices back into the mid to upper 90s, perhaps locally near 100F along the I-95 corridor. As the cold front moves across the region, additional scattered showers and thunderstorms are possible. Storm Prediction Center has placed portions of the region in a Marginal Risk for severe thunderstorms. With surface westerly flow developing today leading to dew points a bit lower than previous days, and weak mid-level lapse rates, environment is not as conducive for widespread activity. That being said, MLCAPE is still progged to reach 1000 J/kg or so, with 35-40 knots of 0-6km overlaid, and with a cold front serving as a focus for convective activity, there is certainly a risk for isolated to scattered severe thunderstorms, with linear segments and localized wind damage being the primary threat. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... Quieter, cooler, and drier weather is expected beginning tonight and lasting through Wednesday night. The aforementioned cold front will continue pushing southeastward and clear the area by Tuesday morning. This will usher in relatively cooler and drier air with dew points falling through the 60s overnight. Lows overnight from the mid 60s to low 70s. High pressure building in behind the front will move from the Great Lakes into the northeastern US Tuesday, leading to northerly surface flow across our region. A mix of sun and fair weather cumulus clouds expected for Tuesday with highs in the 80s and dew points in the low to mid 60s, which will be a noticeable difference. Quiet weather continues Tuesday night with the caveat that there may be some patchy fog and low clouds around early Wednesday morning. Lows Tuesday night in the 60s to near 70F. The high will slide offshore Wednesday with the low level flow turning easterly and then southeasterly. Should see mostly dry conditions, although an isolated shower or thunderstorm can`t be ruled out. Highs will likely actually be a bit below normal for late July, in the low to mid 80s. Potential will exist again for some patchy fog and low clouds Wednesday night into early Thursday morning, but otherwise quiescent weather expected Wednesday night with lows in the 60s to around 70F. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A cold front and its associated upper-level trough will approach the area Thursday into Thursday night before passing through Friday. Warm and humid conditions are expected ahead of the front Thursday. Showers and thunderstorms are possible ahead of the cold front...especially late Thursday into Friday. High pressure may build into the region behind the front...bringing dry...cooler and less humid conditions. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... VFR is expected today. There may be some isolated to scattered showers and thunderstorms later this afternoon and evening. Primarily VFR is then expected overnight through Wednesday night, although we`ll have to monitor for patchy fog and low clouds both Tuesday night and Wednesday night with onshore flow. Showers and thunderstorms are possible ahead of a cold front...mainly late Thursday into Friday. && .MARINE... Small Craft Advisory is in effect through 4 pm across the lower tidal Potomac and portions of the central Chesapeake for gusty southwesterly winds. These winds will diminish late this afternoon with mainly sub-SCA winds expected for the rest of today and through Wednesday night. There may be some isolated to scattered showers and thunderstorms this afternoon and evening. Special Marine Warnings may be necessary. A cold front will approach the waters Thursday into Thursday night before passing through Friday. Showers and thunderstorms are possible ahead of the front...especially late Thursday into Friday. A Small Craft Advisory may be needed for portions of the waters Thursday and Friday. High pressure may return for the weekend. && .TIDES/COASTAL FLOODING... Coastal Flood Advisories in effect for the District of Columbia this morning. No other tidal issues expected at this time. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 11 AM EDT this morning for DCZ001. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ534- 537-543. && $$ UPDATE...WOODY! PREVIOUS...MJM/BJL

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